Executive brief
MasterStudy LMS is a WordPress plugin that provides learning management system functionality, including paid course enrollment. The plugin fails to properly validate payment notifications from PayPal, allowing attackers to bypass payment requirements entirely. An unauthenticated attacker can gain full access to paid courses by making only a minimal token payment, causing direct financial loss and unauthorized access to premium educational content.
Technical details
The vulnerability is a broken access control issue (CWE-284) in the PayPal Instant Payment Notification (IPN) handler. The plugin accepts payment notifications without verifying the amount, receiver, currency, or payment status against the order details. An unauthenticated attacker can craft a valid IPN callback (using a genuine minimal PayPal payment) with an invoice ID pointing to a full-price order; the plugin marks that order completed without amount validation. No authentication is required, only that a PayPal gateway is configured and a paid course exists. The vulnerability is fixed in version 3.7.40.
Affected products
- MasterStudy LMS before 3.7.40
Timeline
- 2026-08-27: disclosed
- 2026-08-29: patched: Fixed in version 3.7.40